Layered, composite, and doped thermal barrier coatings exposed to sand laden flows within a gas turbine engine: Microstructural evolution, mechanical properties, and CMAS deposition

Physical aspects of CMAS particle dynamics and deposition in turboshaft engines

“…These challenges are associated with describing the behavior and evolution of the droplet transport across multiple regimes, phase interface from the molecular scale (e.g., at the contact line), to the transport of a heterophase dispersed phase, to the description of larger anisotropic flow structures, and their mutual interactions. The development of a computational framework must be augmented concurrently with physio-chemical property uncertainty quantification which strongly impacts the adhesion and deposition characteristics [4]. Direct simulations across the full spectrum of spatiotemporal scales, and encompassing all of the physics, in a unified framework is not affordable now and will remain inaccessible in the foreseeable future.…”

“…Operating at such conditions introduces various thermophysical and thermochemical challenges that significantly affect the character of the CMAS particleladen flow and its interaction with engineered protective materials such as thermal and environmental barrier coatings (T/ EBCs). Once ingested, the particulates exposed to the harsh combusting environment undergo phase transformation to melt, with the possibility of CMAS depositing and reacting with the coatings on the combustor liner, turbine shroud, blades, and nozzle guide vanes [3,4]. The ingested particulates also get into the bleed air intake from the compressor and settle mostly as unreacted but sintered sand in the cooling channels in the turbine vanes and blades.…”

Sand corrosion, thermal expansion, and ablation of medium‐ and high‐entropy compositionally complex fluorite oxides

“…Various efforts have suggested that rare earth elements may provide more chemical stability in molten sand environments due to crystallization of the melt, which halts further penetration. 7,[14][15][16][17] Further analysis has suggested that substituting ions with a large radius into the coating material creates a stronger tendency for crystallization. 18 High-entropy alloys (HEAs) emerged in 2004 in the metallurgy community.…”

Adhesion behavior of calcia–magnesia–alumino–silicates on gadolinia-yttria-stabilized zirconia composite thermal barrier coatings

“…Previous work by the authors indicated that an 8 wt% YSZ coating topped by a thin, non-continuous gadolinia (Gd 2 O 3 ) layer exhibited excellent CMAS resistance while retaining much of the favorable mechanical properties of the YSZ [25,26]. While it was originally hypothesized that a thin gadolinia layer would act as a sacrificial reaction layer with the adherent CMAS glass, results indicated otherwise; the mitigation mechanism does not appear to be the formation of an arresting crystallization front (similar to GZO).…”

“…Further investigations into determining the mitigation mechanism along with improving the durability of the coating hetero-structure led to the development of a blended gadolinia-YSZ coating. This approach takes advantage of the excellent damage tolerance and low thermal conductivity of YSZ and the observed CMAS-tolerance of a rare-earth oxide, gadolinia [25,26]. This paper discusses the possible mechanisms that prevent CMAS from adhering to the composite coating.…”